Washington’s influence class lined up against the deficit-reduction supercommittee as the dozen lawmakers charged with cutting as much as $1.5 trillion over a decade scrambled to write ground rules in advance of Thursday’s first public meeting of the panel.

The lobbying is coming from all sides as a wide range of agencies and interest groups look to protect their turf.

The Defense and State departments — and their allies in Congress and on K Street — are warning that steep cuts could endanger national security. Powerful players in the health sector are calculating that they face less exposure if the supercommittee fails and automatic cuts to Medicare — limited to about 2 percent by the new debt-limit law — are imposed. Even Washington’s cottage industry of “good government” groups are leaning on lawmakers to conduct the kind of public deliberations that some insiders think would make it impossible for the supercommittee to make a deal.

If these interests have their way, the supercommittee will be smothered before it takes its first breath.

“We’re conscious of all of that,” Washington Sen. Patty Murray, the Democratic co-chairwoman of the supercommittee, said of the concerns expressed by Defense Secretary Leon Panetta, Secretary of State Hillary Clinton and others over national security cuts.

Democratic and Republican supercommittee members huddled separately on Capitol Hill Wednesday to vet proposed rules for the panel and plot strategy.

Republican leaders lent their imprimatur — and made clear they will stay close to the discussions — by meeting with the GOP supercommittee members Wednesday in the Cannon House Office Building.

“We’re committed that this committee get an outcome, and we believe that by reducing our debt, we create a better environment to create jobs in America,” Speaker John Boehner said afterward. “We’ve talked about this all year; we believe as strongly about it today as we did then. And this is a serious effort that is under way. We’re taking it that way, and we’re encouraging our members to work hard to get it enacted.”

Murray expressed cautious optimism that the panel will get its work done.

“We all very much recognize that the public wants us to solve these critical problems in a serious way,” she said. “There’s no easy solution to this. We’re going to have to make some hard decisions.”

The committee is already facing opposition from agencies and interest groups that figure they could be on the losing end if those hard decisions are made.

The Defense Department’s official play is nuanced: The Pentagon wants to avoid automatic cuts that would account for nearly half of the $1.5 trillion deficit-reduction goal if the supercommittee fails but also persuade the panel not to target the Pentagon in its deliberations. The unofficial fallback plan: The Defense Department, lawmakers that oversee the Pentagon and wealthy defense contractors might well be able to get Congress to block the automatic cuts, which wouldn’t take place until 2013.

Panetta and House Armed Services Committee Chairman Buck McKeon (R-Calif.) are coordinating efforts to spare the Pentagon, according to McKeon, who has a group of about 30 lawmakers, mostly Republicans, ready to fend off any ambitious supercommittee cuts.

“He’s reached out more than I would have expected,” McKeon said of Panetta. “He doesn’t want to be the secretary who hollows out the military.”

Panetta said Tuesday that it will be difficult to cut the Pentagon’s budget without harming the country.

“Clearly, we are facing a crisis because of these huge deficits that the country is facing, and clearly defense is going to have to play a role in trying to achieve whatever savings we can achieve without undermining our national defense and our national strength,” Panetta told interviewer Charlie Rose. “That’s going to be the challenge.”

Panel members also are well aware of a hardening conventional wisdom that the health care industry is better off if the supercommittee can’t reach an agreement. That’s because the debt-limit deal shielded Medicaid from the automatic cuts — that would be implemented if the supercommittee doesn’t meet its target and limited the pain that could be felt by providers of services under Medicare.

Even some of the members of the supercommittee, several of whom serve in the leadership in their respective parties and chambers, have begun drawing lines in the sand.

“If either outside forces or the president or even members of Congress were to force the committee members into situations where you have to compromise our principles, that’s going to be very, very hard to do,” said Arizona Republican Sen. Jon Kyl, one of the 12 negotiators. “On the other hand, if we can find ways to achieve a $1.5 trillion in savings that do not force us to compromise our principles, then maybe we’ll have an easier job of doing that.”

The panel’s target is between $1.2 trillion and $1.5 trillion. If it produces a law that falls short, the difference will be made up by automatic cuts, according to the debt-limit law. But there’s nothing preventing the panel from writing a deficit-reduction measure that exceeds the target.

Democratic staff members on the House Ways and Means Committee have already found more than $500 billion in potential savings from Medicare. Their ideas, which includes an increase in the eligibility age from 65 to 67, is just one of several recommendations the supercommittee could get from standing legislative committees before a mid-October deadline. Sen. Orrin Hatch, the top Republican on the Finance Committee, has said he intends to submit recommendations to the supercommittee.

Some members of that panel have already begun discussing whether to “go big” and shoot for a much larger package than the $1.2 trillion to $1.5 trillion target.

But on Wednesday, the main business was settling on rules before they are voted on at the panel’s first public meeting.

The two sets of lawmakers exchanged their preferences for the rules through their aides, as they had been for days prior to Wednesday’s meetings. Sources said the rules are likely to be a hybrid of House and Senate committee rules within the structure mandated by the debt-limit law.

But the hours of meetings suggested it was not an easy process.

Still, the lawmakers themselves expressed optimism that they would be ready to move forward on Thursday.

“We are a unique committee and working together to make sure we put together a process that helps us move forward to a final resolution [is] what we are all focused on,” Murray said.

Even some who hope to avoid the knife said they expect a few surface wounds.

When asked what he would recommend to the supercommittee, McKeon quickly responded, “Leave us alone,” before acknowledging that “there are going to be some more cuts.”